Currently, no practical method exists for direct measurement of force production from individual muscles during dynamic human movement. Manual muscle tests do not give an accurate estimate of muscle strength which can predict the ability to walk. Measurements of joint torque are inadequate because several muscles often contribute to torque development. Implantation of a buckle transducer on a tendon is highly invasive and impractical for regular use. The integrated electromyogram is customarily used to provide quantification of muscle contraction. However, the problem remains that the electromyographic activity cannot provide a quantitative measure of muscle tension under dynamic conditions. An alternative, measurable parameter related to muscle force is intramuscular pressure. Commercially available intramuscular pressure transducers are too large for optimum comfort. Microsensor technology is now available to construct transducers that are approximately the same size as the fine wires used for electromyographic analysis. The overall objective of this project is to develop and test a fiber optic microsensor that can be used for routing, clinical measurement of muscle function. The specific aims of this study are a) to continue development of a fiber optic microsensor to measure intramuscular pressure, b) to determine the relationships between intramuscular pressure, muscle sarcomere length, and muscle tension under isometric and dynamic conditions for normal muscle in an animal model, and c) to develop a mathematical model of intramuscular pressure in order to establish a theoretical basis for understanding the experimental measurements. The hypothesis examined by this study is that intramuscular pressure is directly related to two independent phenomena; namely, passive elongation of muscle fibers and active force generation by muscle fibers. Successful development of this microsensor will result in a powerful new tool for quantifying muscle function. This device will be useful in offering a better representation of muscle tension under dynamic conditions. It will become an essential tool in clinical gait analysis aimed at improving mobility of disabled patients with neuromuscular disorders such as cerebral palsy, muscular dystrophy, amyotrophic lateral sclerosis, stroke, head injury, spinal cord injury, and poliomyelitis. The ultimate goal is to use this microsensor for clinical decision making to improve the mobility of disabled individuals.